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Unhexbium
Unhexbium, Uhb, is the temporary name for element 162. NUCLE)ilSince at least two sets of predictions exist for location of the neutron dripline up to Z = 175(1),(2), the outer boundary derived in "The Final Element" (this wiki) is too crude to add anything to what is known about Uhb. The inner boundary described in that wiki is more reliable. It indicates that Uhb isotopes are possible within the band ranging from Uhb 367 to Uhb 555. (In this case Uhb 555 may not be the actual upper bound. See "Unhexquadium", this wiki, for details.). All isotopes of Uhb require at least 2.8 MeV of structural correction in order to survive long enough to beta-decay. We know little about structural correction values, except for predictions of shell closure locations. A neutron shell closure has been predicted at N = 370(2), which implies that Uhb isotopes in the vicinity of Uhb 532 may beta decay. A proton shell closure has also been widely predicted to occur at Z = 164, which may extend the range of beta-decaying Uhb isotopes beyond what the neutron shell closure would cause. At least one model exists predicting the half-lives and decay modes for nuclides up to Z = 175 and N = 333(3), which includes isotopes Uhb 495 and lighter. It is helpful to view p 18 of Ref. 3, which maps predicted half-lives of nuclides in this region, and p 15, which maps principal decay modes. Uhb itself needs to be seen in context of the whole nuclear map of its surroundings. The map predicts a band of nuclides ranging from Uhb 435 to Uhb 471. As neutron count increases in this band, half-life increases, reaching a maximum which probably exceeds a second and may be as much as 1000 sec. (The map does not provide mode or half-life information for nuclides which are stable against beta decay.) Principal decay mode shifts from fission, to alpha emission, then to beta emission. This pattern appears to be what is expected from a neutron shell closure at N = 308. However, there is also a band of comparatively stable alpha-decaying isotopes predicted to lie between Uhb 472 and Uhb 482 which do not appear to be stabilized by N = 308. A neutron shell closure has also been predicted to occur at N = 318(4) and a proton shell closure has been predicted at Z = 154(2). Uhu 471 to Uhu 481 may indicate effects of those two closures, as well as N = 308 and Z = 164. ATOMIC Several predictions for the ground state electron structure of Uhb agree that it will have transition metal character, with 7d and 9s electrons available for bonding. Electrons in Uhb can be described in terms of time-independent orbitals, but calculation of electron properties require that nuclear charge be distributed over the nucleus' actual volume. In addition, there is some chance that differing nuclear shapes may produce different electron configurations in different isotopes. (Different isotopes would be different elements in the chemical sense.) Except in the laboratory, Uhb is expected to exist only in environments too hot for ordinary chemistry to occur. FORMATION Neutron capture cannot produce nuclides much larger than A = 500, since fission is expected even at the inner dripline above this point. As material originally from 800 – 1000 m deep within a neutron star is forced outward when the star disintegrates during a merger, large drops of nuclear matter located near the inner neutron dripline will probably appear. Where stabilized by around 3 MeV by the nearby presence of a shell closure, these drops may be beta-decaying nuclides, which can subsequently evolve toward higher Z until they reach nuclides which fission. Such a band, anchored by N = 370, may allow isotopes in the Uhb 520 to Uhb 540 range to form. Fission (especially from excited daughters) will compete with beta decay during evolution to Uhb, which may greatly reduce the amount which forms. Fission and multinucleon transfer reactions occurring in the polar jets emanating from neutron stars and black holes may allow isotopes in the band Uhb 370 to Uhb 500 to form. Quantities produced in this way are tiny. REFERENCES 1. "Neutron and Proton Drip Lines Using the Modified Bethe-Weizsacker Mass Formula; D.N. Basu et al; Int.J.Mod.Phys.; arXiv:nucl-th/0306061; url: https://arxiv.org/abs/nucl-th/0306061 2. “Single Particle Levels of Spherical Nuclei in the Superheavy and Extremely Superheavy Mass Region”; H. Koura and S. Chiba; Journal of the Physical Society of Japan; DOI 10.7566/JPSJ.82.014201; Jan. 2013. 3. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011. 4. “The Highest Limiting Z in the Extended Periodic Table”; Y.K. Gambhir, A. Bhagwat, and M. Gupta; Journal of Physics G: Nuclear and Particle Physics. 42 (12): 125105. DOI:10.1088/0954 3899/42/12/ 125105. (12-30-19)